1. Field of the Invention
The present invention relates to a washing machine, and particularly, to a method and an apparatus for detecting a laundry weight of a washing machine.
2. Description of the Background Art
In general, a washing machine is a device for washing laundry by performing a washing process, a rinsing process and a dewatering process. The washing machine is classified into a pulsator type, an agitation type, a drum type or the like according to washing methods. Also, the washing machine measures the laundry weight and the amount of eccentricity, and the laundry weight is an important factor to determine a dewatering speed.
FIG. 1 is a view showing a waveform for determining a laundry weight value by using a method of detecting the laundry weight of a washing machine in accordance with the conventional art.
As shown therein, in a method for detecting a laundry weight of a washing machine in accordance with the conventional art, a motor is driven twice at the same speed for the same time, and then a laundry weight of a washing machine is calculated based on an average value of a current needed to drive the motor, an average value of the amount of eccentricity according to a variation of a motor speed and a supply voltage compensation value. Here, the average value of the current is an average value of a current applied to the motor while the motor is driven at the same speed.
In addition, the amount of eccentricity is measured by using the size of a speed ripple, which has detected through a speed sensor. Namely, a speed data (vk) is measured every certain angle (e.g., an angle of 30°), and an acceleration data (ak) is obtained by subtracting the sum total of first six speed data (vk-6+vk-7+vk-8+vk-9+vk-10+vk-11) which have previously measured from the sum total of another six speed data (vk+vk-1+vk-2+vk-3+vk-4+vk-5). Here, when twelve acceleration data each of which is obtained when a drum of a washing machine rotates once are obtained, a minimum value of the data is subtracted from their maximum value, thereby obtaining the amount of eccentricity. The amount of eccentricity can be denoted as the following Equation 1 and 2.ak=(vk+vk-1+vk-2+vk-3+vk-4+vk-5)−(vk-6+vk-7+ . . . vk-11)  Equation 1Amount of eccentricity=max(a1,a2, . . . a12)−min(a1,a2, . . . a12)  Equation 2
Accordingly, a final laundry weight of a washing machine is obtained by the following Equation 3 based on an average value of a first laundry weight and a second laundry weight, first amount of eccentricity and second amount of eccentricity, and a supply voltage compensation value.Final laundry weight value=(first laundry weight+second laundry weight)/2+supply power compensation value−(first amount of eccentricity+second amount of eccentricity)+k1  Equation 3
Here, the first laundry weight is an average value of a current for first ‘a’ seconds, and the second laundry weight is an average value of a current for second ‘a’ seconds. The first amount of eccentricity is the average amount of eccentricity for first ‘a’ seconds, and the second amount of eccentricity is the average amount of eccentricity for second ‘a’ seconds. In addition, the supply voltage compensation value=(detected supply voltage value−k2)*k3, the eccentricity compensation value=(first eccentricity+second eccentricity)/2}*k4, and k1˜k4 are scale values set arbitrarily in order to determine the laundry weight.
Hereinafter, laundry weight values by laundry, which are measured by using a method for detecting the laundry weight in accordance with a different conventional art will now be described with reference to FIG. 2.
FIG. 2 is a view showing laundry weight values by laundry, which are measured by a method for detecting a laundry weight in accordance with the different conventional art.
As shown therein, in the method for detecting the laundry weight of a washing machine in accordance with the different conventional art, the laundry weight of the washing machine is calculated by using an average value of a current applied to a motor of the washing machine, an average value of the amount of eccentricity and a compensation value of a supply voltage. Here, in order to obtain the amount of eccentricity generated when the washing machine dewaters the laundry, speed data are measured every certain electrical angle, and an acceleration is obtained by using the sum total of the speed data and the sum total of previous speed data. Then, based on a maximum value and a minimum value of the acceleration data, the amount of eccentricity is calculated. However, the method has a problem in that a motor of a washing machine employing an correctly-designed current/speed control system has a small speed variation, which causes incorrect measuring of the amount of eccentricity.
In addition, when the laundry weight is detected by using a compensation value of a supply voltage, if a supply voltage is not constantly supplied, a different supply voltage value is compensated for the same load. Accordingly, it is difficult to obtain a correct laundry weight.
In addition, the method for detecting the laundry weight in accordance with the conventional art has a problem in that a weight of wet laundry cannot be correctly detected because a laundry weight is obtained based on dry laundry.
Detailed description on washing machine in accordance with conventional arts is disclosed in U.S. Pat. No. 6,615,619 and No. 6,612,138.